[Experimental studies on peripheral nerve injuries caused by injection needles]

Differences in neural damage due to different injection needles were investigated in vitro on sciatic nerve specimens of adult rabbits. METHODS. Three types of 22-gauge needles were tested: one typical, long-bevelled venous puncture needle; a short bevelled, typical nerve block needle; and a tapered, atraumatic spinal needle. Both sciatic nerves of 50 adult rabbits weighing from 2.5 to 3.0 kg were used for electrophysiological investigations on one side and fluorescence microscopy on the other. ELECTROPHYSIOLOGY. The nerve specimens were placed in an experimental chamber on silver-silver chloride electrodes that were aligned at a distance of 10 mm. Two electrodes at the distal ends of the nerve were used for stimulation by rectangular waves (6-10 v) of 0.01 ms duration. The compound action potential (CAP), its amplitude, and its latency were measured by monopolar recording from four additional electrodes (R1 to R4). Ten nerves were apportioned to each of five groups and the needles were perpendicularly pierced three times in the middle of the nerve trunk at the midpoint between recording sites R2 and R3. THE GROUPS. 1. Long-bevelled needle, the face of the bevel inserted rectangular to the nerve fibers; 2. long-bevelled needle, the face of the bevel parallel to the nerve fibers; 3. short-bevelled needle, the face of the bevel inserted rectangular to the nerve fibers; 4. short-bevelled needle, the face of the bevel parallel to the nerve fibers; 5. tapered, pencil-point needle pierced perpendicularly through the nerve trunk. The amplitude of the CAP was recorded before and after nerve injury from R1 to R4. FLUORESCENCE MICROSCOPY. According to the method described by Steinwall and Olsson, the other five groups of injured nerves were immersed in Evans blue albumin (EBA) and, after washing in saline solution, fixed in 5% formalin. The extent of nerve damage was evaluated by fluorescence microscopy of the glycerol-imbedded frozen sections (longitudinal and transverse). RESULTS. Electrophysiology. After injuring the area between R2 and R3 there was almost no change in the amplitude of the CAP at sites R1 and R2. The amplitude at R3 and R4 was reduced in comparison with the controls. This reduction was most marked in group 1 and very slight in group 5. The percentages of amplitude at R3 after injury compared with control values (mean +/- SD) were 42.2% +/- 22.0% in group 1; 60.9% +/- 18.2% in group 2; 51.0% +/- 22.3% in group 3; 71.0% +/- 18.0% in group 4; and 90.1% +/- 10.9% in group 5. Statistically significant differences were obtained between the tapered, atraumatic needle group and the other four groups (Fig. 3). Fluorescence microscopy. With the tapered injection needle there was the least leakage of EBA, which suggests the least damage to the perineurium, and almost no rupture or tearing of the nerve fibers was observed. In the short- and long-bevelled needles, the damage was reduced when the face of the bevel was inserted parallel to the fibers.